Quantum Networks Research

A quantum network is a network of entangled states. These states can carry quantum information from one place to another. Entanglement means two particles stay linked, however far apart they are.

Why does that matter?

Think of two magic coins. Flip one in Delhi and the other in Kolkata always shows a matching result. Nobody can say the result before the flip. Yet the two coins stay linked. Entangled particles behave a little like this pair.

What is the memory hook?

Think “linked particles, far apart”.

QKD stands for Quantum Key Distribution. It lets two parties share a secret key. The key then locks and unlocks their messages.

What makes it safe?

Think of a letter sealed with wax. If anyone opens it, the seal is broken. You see the damage at once. A quantum signal works the same way. Measuring it changes its state. The two legitimate users can spot the change.

• Any attempt to intercept the photons disturbs them.
• The users then know a spy is present.
• Entanglement-based QKD stays secure even if the hardware is faulty or compromised.
• Older prepare-and-measure methods do not offer that extra protection.

What is the memory hook?

Think “look and you leave a mark”.

In February 2022, India showed its first QKD link between two cities. A joint team from DRDO and IIT Delhi built it. DRDO is the Defence Research and Development Organisation.

What were the key facts?

• The link joined Prayagraj and Vindhyachal in Uttar Pradesh.
• The distance was more than 100 kilometres.
• It ran over ordinary commercial-grade optical fibre already laid in the field.
• DRDO announced it on 23 February 2022.
• DRDO said it proved indigenous technology for sharing secure keys.

What is the memory hook?

Think “2022, two cities, fibre”.

Free-space QKD sends quantum signals through open air. It needs no optical fibre. In June 2025, DRDO and IIT Delhi tested it using entanglement.

What did the test show?

• The link covered more than 1 kilometre on the IIT Delhi campus.
• The secure key rate was nearly 240 bits per second.
• The quantum bit error rate (QBER) was under 7%. QBER is the share of key bits that arrive wrong.
• The DRDO-Industry-Academia Centre of Excellence (DIA-CoE) at IIT Delhi ran the test.
• The research group of Prof Bhaskar Kanseri led the work.

Why is no fibre useful?

Laying cable is costly. It is also hard across rough ground. A beam through air skips that work.

What is the memory hook?

Think “air, not cable”.

QNu Labs, BISAG-N and IIT Gandhinagar ran a free-space QKD link over 5.56 kilometres. It was India’s first such link at this distance. BISAG-N is the Bhaskaracharya National Institute for Space Applications and Geo-informatics.

What were the key facts?

• The trial ran overnight on 27-28 September 2026.
• It linked BISAG-N and IIT Gandhinagar through open air.
• The QBER stayed below 5%.
• The secure key rate was 230 to 260 bits per second.
• That is about one fresh 256-bit key every second.

Where did the keys go?

The keys went into BISAG-N’s Vedic Kavach platform. It uses post-quantum cryptography (PQC). PQC means ordinary maths-based codes built to resist quantum computers. So hardware and software protection worked together.

What is the memory hook?

Think “5.56 km, night, Vedic Kavach”.

GCP stands for General Concurrence Percolation. Two Bose Institute scientists, Dr Deep Nath and Prof Soumen Roy, proposed it. The Bose Institute is an autonomous institute under the Department of Science and Technology.

What problem does it solve?

Entanglement is hard to keep strong over long distances. Older methods tried to fix this by removing some intermediate stations. That wastes resources and changes the network.

How does GCP differ?

• It uses geometric routing and removes no nodes.
• It strengthens entanglement along the shortest available paths.
• Computer simulations showed it lowers the entanglement needed to connect the whole network.
• It is a theory result. It is not a working hardware link.

When was it published?

The paper is in Physical Review A, volume 114, article 012440. The journal published it on 16 July 2026. News reports followed in August 2026.

What is the memory hook?

Think “route smartly, remove nothing”.

Four mix-ups come up again and again.

What are the traps?

• Fibre or air? The 2022 link used fibre. The 2025 and 2026 links used open air.
• Which distance? The 2022 link was over 100 km. The 2025 link was over 1 km. The 2026 link was 5.56 km.
• Which team? DRDO and IIT Delhi did 2022 and 2025. QNu Labs, BISAG-N and IIT Gandhinagar did 2026.
• Link or theory? GCP is a simulated protocol. The other three are field tests.

How do you remember them?

Think “fibre first, then air, then theory”.